I got this one and have been very happy with it: https://www.amazon.com/gp/product/B010A5JBPO/ref=ppx_yo_dt_b_search_asin_image?ie=UTF8&psc=1
Works with a 12V car plug, and also comes with an AC adapter. Great to use on a cold morning for dry boots too. They'll be nice and toasty after a 15-20 minute drive to the mountain.